The present invention generally relates to spinal implants. Specifically, the present invention relates to implantable devices and methods for the treatment of spinal disorders associated with the intervertebral disc.
Back pain is one of the most common and often debilitating conditions affecting millions of people in all walks of life. Today, it is estimated that over ten million people in the United States alone suffer from persistent back pain. Approximately half of those suffering from persistent back pain are afflicted with chronic disabling pain, which seriously compromises a person""s quality of life and is the second most common cause of worker absenteeism. Further, the cost of treating chronic back pain is very high, even though the majority of sufferers do not receive treatment due to health risks, limited treatment options and inadequate therapeutic results. Thus, chronic back pain has a significantly adverse effect on a person""s quality of life, on industrial productivity, and on heath care expenditures.
Some forms of back pain are not chronic and may be simply treated by rest, posture adjustments and painkillers. For example, some forms of lower back pain (LBP) are very common and may be caused by unusual exertion or injury. Unusual exertion such has heavy lifting or strenuous exercise may result in back strain such as a pulled muscle, sprained muscle, sprained ligament, muscle spasm, or a combination thereof. An injury caused by falling down or a blow to the back may cause bruising. These forms of back pain are typically non-chronic and may be self-treated and cured in a few days or weeks.
Other types of non-chronic back pain may be treated by improvements in physical condition, posture and/or work conditions. For example, being pregnant, obese or otherwise significantly overweight may cause LBP. A mattress that does not provide adequate support may cause back pain in the morning. Working in an environment lacking good ergonomic design may also cause back pain. In these instances, the back pain may be cured by eliminating the culprit cause. Whether it is excess body weight, a bad mattress, or a bad office chair, these forms of back pain are readily treated.
However, some forms of back pain are chronic and are the result of spinal disorders which are not readily treated. Such spinal disorders may cause severe back pain, the origin of which may or may not be certain. A prevalent clinical theory is that pain arises from physical impingement of the nerve roots or the spinal cord. Such nerve impingement may have of a number of different causes, but generally results from either a disc protrusion or from narrowing of the intervertebral foramina which surround the nerve roots. Another clinical theory is that damage to the disc, either from injury, degradation or otherwise, causes physical impingement of the disc nerves, which are primarily disposed about the periphery of the annulus, but may grow into fissures of a damaged disc.
Disc protrusions may be caused by a physical injury to the disc or by natural degradation of the disc such as by degenerative disc disease (DDD). Physical injury may cause damage to the annulus fibrosus which allows a portion of the disc, such as the nucleus pulposus, to protrude from the normal disc space. DDD may cause the entire disc to degenerate to such a degree that the annulus fibrosus bulges outward, delaminates or otherwise separates such that a portion of the disc protrudes from the normal disc space. In either case, the disc protrusion may impinge on a spinal nerve root causing severe pain. Impingement on the nerve root may also be caused by conditions unrelated to the disc such as by a spinal tumor or spinal stenosis (abnormal bone growth), but disc protrusions are the most common cause. Depending on the cause and nature of the disc protrusion, the condition may be referred to as a disc stenosis, a disc bulge, a herniated disc, a slipped disc, a prolapsed disc or, if the protrusion separates from the disc, a sequestered disc.
Nerve root impingement most often occurs in the lumbar region of the spinal column since the lumbar discs bear significant vertical loads relative to discs in other regions of the spine. In addition, disc protrusions in the lumbar region typically occur posteriorly because the annulus fibrosus is thinner on the posterior side than on the anterior side and because normal posture places more compression on the posterior side. Posterior protrusions are particularly problematic since the nerve roots are posteriorly positioned relative to the intervertebral discs. When a posterior disc protrusion presses against a nerve root, the pain is often severe and radiating, and may be aggravated by such subtle movements as coughing, bending over, or remaining in a sitting position for an extended period of time.
A common treatment for disc protrusion is discectomy, which is a procedure wherein the protruding portion of the disc is surgically removed. However, discectomy procedures have an inherent risk since the portion of the disc to be removed is immediately adjacent the nerve root and any damage to the nerve root is clearly undesirable. Furthermore, discectomy procedures are not always successful long term because scar tissue may form and/or additional disc material may subsequently protrude from the disc space as the disc deteriorates further. The recurrence of a disc protrusion may necessitate a repeat discectomy procedure, along with its inherent clinical risks and less than perfect long term success rate. Thus, a discectomy procedure, at least as a stand-alone procedure, is clearly not an optimal solution.
Discectomy is also not a viable solution for DDD when no disc protrusion is involved. As mentioned above, DDD causes the entire disc to degenerate, narrowing of the intervertebral space, and shifting of the load to the facet joints. If the facet joints carry a substantial load, the joints may degrade over time and be a different cause of back pain. Furthermore, the narrowed disc space can result in the intervertebral foramina surrounding the nerve roots to directly impinge on one or more nerve roots. Such nerve impingement is very painful and cannot be corrected by a discectomy procedure.
As a result, spinal fusion, particularly with the assistance of interbody fusion cages, has become a preferred secondary procedure, and in some instances, a preferred primary procedure. Spinal fusion involves permanently fusing or fixing adjacent vertebrae. Hardware in the form of bars, plates, screws and cages may be utilized in combination with bone graft material to fuse adjacent vertebrae. Spinal fusion may be performed as a stand-alone procedure or may be performed in combination with a discectomy procedure. By placing the adjacent vertebrae in their nominal position and fixing them in place, relative movement therebetween may be significantly reduced and the disc space may be restored to its normal condition. Thus, theoretically, aggravation caused by relative movement between adjacent vertebrae (and thus impingement on the nerve root by a disc protrusion and/or impingement from bone may be reduced if not eliminated.
However, the success rate of spinal fusion procedures is certainly less than perfect for a number of different reasons, none of which are well understood. In addition, even if spinal fusion procedures are initially successful, they may cause accelerated degeneration of adjacent discs since the adjacent discs must accommodate a greater degree of motion. The degeneration of adjacent discs simply leads to the same problem at a different anatomical location, which is clearly not an optimal solution. Furthermore, spinal fusion procedures are invasive to the disc, risk nerve damage and, depending on the procedural approach, either technically complicated (endoscopic anterior approach), invasive to the bowel (surgical anterior approach), or invasive to the musculature of the back (surgical posterior approach).
Another procedure that has been less than clinically successful is total disc replacement with a prosthetic disc. This procedure is also very invasive to the disc and, depending on the procedural approach, either invasive to the bowel (surgical anterior approach) or invasive to the musculature of the back (surgical posterior approach). In addition, the procedure may actually complicate matters by creating instability in the spine, and the long term mechanical reliability of prosthetic discs has yet to be demonstrated.
Many other medical procedures have been proposed to solve the problems associated with disc protrusions. However, many of the proposed procedures have not been clinically proven and some of the allegedly beneficial procedures have controversial clinical data. From the foregoing, it should be apparent that there is a substantial need for improvements in the treatment of spinal disorders, particularly in the treatment of nerve impingement as the result of damage to the disc, whether by injury, degradation, or the like.
The present invention addresses this need by providing improved devices and methods for the treatment of spinal disorders. As used herein, the term spinal disorder generally refers to a degradation in spinal condition as the result of injury, aging or the like, as opposed to a spinal deformity resulting from growth defects. The improved devices and methods of the present invention specifically address nerve impingement as the result of damage to the disc, particularly in the lumbar region, but may have other significant applications not specifically mentioned herein. For purposes of illustration only, and without limitation, the present invention is discussed in detail with reference to the treatment of damaged discs in the lumbar region of the adult human spinal column.
As will become apparent from the following description, the improved devices and methods of the present invention reduce if not eliminate back pain while maintaining near normal anatomical motion. Specifically, the present invention provides dynamic bias devices and reinforcement devices, which may be used individually or in combination, to eliminate nerve impingement associated with a damaged disc, and/or to reinforce a damaged disc, while permitting relative movement of the vertebrae adjacent the damaged disc. The devices of the present invention are particularly well suited for minimally invasive methods of implantation.
The dynamic bias devices of the present invention basically apply a bias force to adjacent vertebrae on either side of a damaged disc, while permitting relative movement of the vertebrae. By applying a bias force, disc height may be restored, thereby reducing nerve impingement. Specifically, by restoring disc height, the dynamic bias devices of the present invention: retract disc protrusions into the normal disc space thereby reducing nerve impingement by the protrusions; reduce the load carried by the facet joints thereby eliminating nerve impingement originating at the joint; restore intervertebral spacing thereby eliminating nerve impingement by the intervertebral foramina; and reduce pressure on portions of the annulus thereby alleviating nerve impingement in disc fissures.
The reinforcement devices of the present invention basically reinforce a damaged disc, restore disc height and/or bear some or all of the load normally carried by a healthy disc, thereby reducing nerve impingement. Some embodiments of the reinforcement members of the present invention have a relatively small profile when implanted, but are very rigid, and thus serve to reinforce the disc, particularly the annulus. By reinforcing the disc, and particularly the annulus, disc protrusions may reduced or prevented, thereby eliminating nerve impingement by the protrusions. Other embodiments have a relatively large profile when implanted, and thus serve to increase disc height and/or to bear load. By increasing disc height, the advantages discussed previously may be obtained. By bearing some of the load normally carried by a healthy disc, the load may be redistributed as needed, such as when a dynamic bias device is used.